The present invention relates to systems for controlling venting of fuel vapors from a vehicle fuel tank. More particularly, the present invention relates to systems including control valve assemblies for venting fuel vapor from the fuel tank via a first vent path during vehicle operation and for venting fuel vapor from the fuel tank via a second vent path during vehicle refueling.
It is well understood that significant quantities of fuel vapor can escape from a fuel tank through the filler neck to the atmosphere during the refueling of motor vehicles. Early attempts to control the vapor escape focused upon control devices fitted to the fuel dispensing nozzle. Later, control devices mounted directly on-board the vehicle (and thus referred to as "on-board vapor recovery" systems or "OBVR" systems) were developed. See, for example, U.S. Pat. No. 4,836,835, relating to a vacuum-actuated vapor recovery system mounted on the fuel tank filler neck. OBVR systems which mount to the fuel tank have also been developed.
In addition to controlling vapor escape, well-designed OBVR systems also assist in controlling the amount of liquid fuel which can be pumped into the fuel tank during refueling. For safety reasons, fuel systems are designed so that the fuel tank is never completely filled with liquid fuel. Rather, at least a predetermined portion of the fuel tank is left for liquid fuel and fuel vapor expansion. Although fuel pump nozzles typically include sensors for shutting off the flow of liquid fuel into the fuel tank when the fuel tank is nearly filled, fuel pump users may manually override the sensors by continuing to pump fuel after the sensors have automatically shut the pump nozzle off. To assist in preventing tank overfill under such conditions, the OBVR system is usually provided with a fill-limit valve which prevents the escape of vapor through the OBVR system, and thus assists in triggering the nozzle shut-off mechanism, when the level of liquid fuel in the fuel tank has risen to a predetermined level.
It has also long been recognized that fuel vapor is generated in the fuel tank during operation of the vehicle, for example, by evaporation or by sloshing of the liquid fuel against the walls of the tank. Excessive pressure can build up in the fuel tank as a result of the newly-formed fuel vapor unless control devices are provided to vent the fuel vapor from the fuel tank during vehicle operation. Such valves have been referred to as "run-loss" valves or tank venting rollover valves because they handle fuel vapor loss during vehicle run and are capable of preventing liquid fuel carry over during vehicle rollover.
Coincident with developing OBVR systems to handle venting of fuel vapor during refueling, fuel systems engineers pursued advancements in tank pressure control systems, particularly run-loss valves for venting the fuel tank during vehicle operation. One driving force behind such advancements was the need to provide run-loss valves having very large flow capacities. For example, prior valves typically had flow orifices in the range of 0.050 inch diameter or smaller. Current valves might have flow orifice diameters as large as 0.290 inch.
Presumably, one might wish to use a high flow capacity run-loss valve with, for example, a tank-mounted OBVR system including fill limit control to provide a comprehensive vapor recovery and pressure control system. But it is contemplated that a parallel arrangement of the run-loss valve with the OBVR system would prove unacceptable because the two tend to work at odds with one another in controlling overfill of the fuel tank.
During refueling of a fuel tank provided with a parallel arrangement of a run-loss valve and an OBVR system, the fill-limit control valve in the OBVR system will close off the OBVR system, preventing further escape of fuel vapor, when a predetermined amount of liquid fuel has been pumped into the tank. However, the high-flow capacity run-loss valve will tend to remain open, continuing to allow escape of fuel vapor and thus allowing additional liquid fuel to be pumped into the fuel tank. It would thus be desirable to provide a tank venting and vapor recovery system capable of selectively providing venting through either a run-loss valve or an OBVR valve while properly preventing tank overfill.
According to the present invention, an apparatus is provided for controlling discharge of fuel vapors from a vehicle fuel tank having a filler neck. The apparatus is particularly suited for controlling venting of fuel vapor from a first vent valve (for example, a run-loss valve) and a second vent valve (for example, an OBVR system).
In particular, the controlling apparatus comprises a housing defining an interior region. The housing is formed to include first and second inlet ports connecting the interior region in fluid communication with the fuel tank. The housing is also formed to include a signal port connecting the interior region in fluid communication with the filler neck, and an outlet port.
The controlling apparatus further includes a first valve assembly movable between a blocking position and a venting position. When moved to its blocking position, the first valve assembly prevents fuel vapor received from the first inlet port from flowing through the interior region during vehicle refueling. When positioned in the venting position, the first valve assembly allows fuel vapor received from the first inlet port to flow through the interior region to the outlet port during vehicle operation.
The controlling apparatus further includes a signal passageway extending between the filler neck and the signal port to expose the first valve assembly to fuel vapor pressure from the filler neck. Filler neck pressure thus moves the first valve assembly toward its venting position during vehicle operation.
The controlling apparatus further includes a second valve assembly also movable between a blocking position and a venting position. When moved to its blocking position, the second valve assembly prevents fuel vapor received from the second inlet port from flowing through the interior region. Advantageously, the second valve assembly is maintained when the first valve assembly is moved to its venting position during vehicle operation. When the second valve assembly is positioned in its venting position, fuel vapor received from the second inlet port is able to flow through the interior region to the outlet port. Also advantageously, the first valve assembly is maintained in its blocking position when the second valve assembly moves to its venting position during vehicle refueling.
Further advantageously, the first valve assembly is initially actuated to move away from its blocking position by fuel vapor pressure received from the filler neck, but then is further depressed by fuel vapor pressure received from the fuel tank. This helps ensure that the first valve assembly maintains the second valve assembly in its blocking position during vehicle operation.
In accordance with one aspect of the invention, the controlling apparatus further includes a flow tube extending between the first inlet port and the first valve assembly. The flow tube includes a valve seat and the first valve assembly includes a rigid valve body sized to sealingly engage the valve seat. The first valve assembly further includes a flexible member linked to the rigid valve body and deformable under a predetermined amount of fuel vapor pressure received from the signal port to move the rigid valve body out of engagement with the valve seat to place the first valve assembly in its venting position.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.